Many parts of the world lack sufficient rainfall at different times of the year to maintain the health of turf and landscaping. Irrigation systems are therefore used to deliver water to such vegetation from municipal water supplies and wells according to a watering schedule. A typical irrigation system comprises a programmable controller that turns valves ON and OFF to deliver water through a plurality of sprinklers connected to the valves via subterranean pipes. These sprinklers are usually rotor-type, impact, spray, or rotary stream sprinklers. A rotor-type sprinkler includes a riser that houses a turbine and a gear train reduction that rotates a nozzle that typically ejects a relatively large stream of water. The riser can be installed above the ground or the riser can be installed within an outer housing that allows it to pop-up when water pressure is applied.
Unfortunately rotor-type sprinklers do not typically irrigate a given area with matched precipitation rates. A plurality of rotor-type sprinklers installed on the same irrigation site may all have the same size nozzles installed in the same, each emitting the same volume of water per unit of time and distributing that water at a uniform radius. One of these rotor-type sprinklers may be set for one hundred and eighty degrees of coverage, and another of these rotor-type sprinklers may be set for three hundred and sixty degrees of coverage. The landscape watered by the rotor-type sprinkler that is set for one hundred and eighty degrees will receive twice as much water per square foot as the landscape watered by the other rotor-type sprinkler. If another one of the rotor-type sprinklers is set for ninety degrees, the area watered by that rotor-type sprinkler will receive four times as much water per square foot as the area watered by the rotor-type sprinkler set for three hundred and sixty degrees. Thus, the rotor-type sprinklers that are set for a smaller arc may over-water the areas watered by those sprinklers, resulting in a substantial waste of water. To compensate for this, installers may install all of the rotor-type sprinklers set for small arcs on one zone, all of the rotor-type sprinklers set for mid-sized arcs on another zone, and finally all of the rotor-type sprinklers set for full circle rotation on a yet another zone. The installer can then program the zones for different run times to compensate for the different amounts of water applied to the irrigated areas by the rotor-type sprinklers installed in the different zones. This configuration of an irrigation system requires more underground pipes and complex programming of the irrigation controller.
Matched precipitation rate rotary stream sprinklers have been installed in residential and commercial applications. See, for example, U.S. Pat. No. RE40,440 E granted Jul. 22, 2008 to George L. Sesser, and entitled “Micro-Stream Rotator with Adjustment of Throw Radius and Flow Rate”, also assigned to Hunter Industries, Inc. Rotary stream sprinklers of this type have been successfully commercialized by Hunter Industries, Inc. under the MP ROTATOR® trademark. However, rotary stream sprinklers have a limited range or radius and are not suitable for use when large areas of landscape must be watered such as golf courses and playing fields. Another marginal solution to the problem of achieving matched precipitation in a residential or commercial irrigation system that utilizes rotor-type sprinklers is to mix and match nozzles on the irrigation site using lower flow nozzles for the rotor-type sprinklers with smaller arc settings. This requires that the installer possess a high level of skill and adds undue complexity to the irrigation system. Moreover, it is not practical to supply a large selection of nozzles having different flow rates to match, for example, the precipitation from a rotor-type sprinkler set to water over an arc of one hundred and twenty degrees to a rotor-type sprinkler set to water an arc of two hundred and seventy degrees.